An oil base ink can write on both surfaces of ink-absorbing materials such as paper and cloth and ink-non-absorbing materials such as plastics, glass and metal. In addition, since it has a quick drying property, it is widely used as an oil base ink for writing tools.
In particular, since an ink using a pigment as a colorant is excellent in handwriting fastness, it is generally known as a paint marker and used not only in homes, schools and offices but also in various industrial fields. Carbon black is used as a pigment for a black ink.
However, since an oil base pigment ink composition using carbon black does not provide a sufficient discharge amount to writing tools having a discharge mechanism making use of a capillary phenomenon because of a high viscosity thereof and causes writing starving, a valve mechanism is employed in the paint marker to secure the discharge amount.
The ink described above causes phenomena such as flocculation and precipitation of carbon black while being used over a long period of time, which results in deteriorating the fluidity and bringing about clogging at a pen point. Accordingly, conventional paint markers employ a redispersing method in which a stirring member such as a metal ball is put into an ink reservoir together with an ink and have a complicated structure in combination with a valve mechanism, which has brought about problems that many parts are required and that the assembly work steps are complicated and the cost is high.